A number of nuclear cases involve ships or submarines colliding at sea or, in some cases, submarine nuclear power units becoming unstable and the subs having to be abandoned. There have been more than 120 submarine accidents since 1956. The most recent incident, in August 2000, was the loss of the Russian nuclear submarine Kursk in the Barents Sea. The Kursk is the seventh nuclear submarine lost, five of them Russian, two American. There are 92 known cases of nuclear bombs lost at sea.